1. Field of the Invention
This invention relates to switched resistor regulators. More specifically, this invention relates to controlling switched resistor regulators so that control feedback loop gain does not vary excessively with changes in operating voltage.
2. Description of Related Art
A switched resistor regulator ("SRR") is a type of power supply regulator, characterized by switching a resistor into and out of electrical connection between a power source and a load. SRRs and their operation are fully disclosed in U.S. Pat. No. 4,668,906, issued May 26, 1987 in the name of inventor John P. Ekstrand, and assigned to the same assignee. Some applications and improvements with respect to SRRs are disclosed in U.S. Pat. No. 4,719,404, issued Jan. 12, 1988 in the name of inventor John P. Ekstrand, and assigned to the same assignee, and in co-pending applications titled "SWITCHED RESISTOR REGULATOR WITH DIODE SNUBBER FOR PARASITIC INDUCANCE IN SWITCHED RESISTOR", Ser. No. 102,982, filed Sept. 30, 1988 in the name of inventor John P. Ekstrand, and assigned to the same assignee, and titled "SHUNT SWITCHED RESISTOR REGULATOR WITH DIODE SNUBBER", Ser. No. 103,095, filed Sept. 30, 1988 in the name of inventor John P. Ekstrand, and assigned to the same assignee, all hereby incorporated by reference as if fully set forth herein.
Further information on switched resistor regulators and their use is found in a co-pending application titled "SWITCHED RESISTOR REGULATOR CONTROL WHEN TRANSFER FUNCTION INCLUDES DISCONTINUITY", Ser. No. 269,238, filed this same day in the name of inventor John P. Ekstrand, and assigned to the same assignee, hereby incorporated by reference as if fully set forth herein.
A typical SRR employs a pulse-width modulator ("PWM") to generate a pulse train, which is applied to the switch for switching the resistor into and out of electrical connection. A feedback loop is employed to assure that the pulse train generated by the PWM switches the resistor at a duty cycle which preserves the indicated operating voltage and/or current. A problem arises when it is desired to operate the SRR at operating conditions which are widely varying. Because the SRR has a nonlinear response to changes in control voltage, the gain from the control voltage to the output voltage and/or current may differ at different operating conditions. This difference can be substantial when the operating conditions are substantially different.
In such cases, the feedback control loop employed by the SRR for stabilizing the duty cycle of the resistor will be subject to a problem. While it is not difficult to adjust for operating parameters (e.g. speed of response and reduction of ripple) which are optimum at any fixed operating point, it is difficult to select operating parameters which will be optimum (or nearly so) at operating voltages which are widely varying, precisely because the gain of the feedback control loop differs at different operating voltages. This effect is well known in the art of feedback regulative control. Inability to select those operating parameters which are preferred can degrade the performance of systems whose power is being supplied by the SRR.